Uniaxial tension focus mask for a color CRT with electrical connection means

ABSTRACT

A color cathode-ray tube 10 has an evacuated envelope 11 with an electron gun 26 therein for generating at least one electron beam 28. The envelope further includes a faceplate panel 12 having a luminescent screen 22 with phosphor lines on an interior surface thereof. A uniaxial tension focus mask 25, having a plurality of spaced-apart first metal strands 40, is located adjacent to an effective picture area of the screen 22. The spacing between the first metal strands 40 defines a plurality of slots 42 substantially parallel to the phosphor lines of the screen. A plurality of second metal strands 60 are oriented substantially perpendicular to the first metal strands 40 and are insulated therefrom across the effective picture area by insulators 62. The second metal strands 60 are attached by a glass conductor layer 68 to respective right and left first metal end strands 140 outside the effective picture area to form busbars.

This invention relates to a color cathode-ray tube (CRT) and, moreparticularly, to a color CRT having a uniaxial tension focus mask havingan efficient structure for making electrical connections thereto.

BACKGROUND OF THE INVENTION

A conventional shadow mask type color CRT generally comprises anevacuated envelope having therein a luminescent screen with phosphorelements of three different emissive colors arranged in color groups, ina cyclic order, means for producing three convergent electron beamsdirected towards the screen, and a color selection structure, such as amasking plate, between the screen and the beam-producing means. Themasking plate acts as a parallax barrier that shadows the screen. Thedifferences in the convergence angles of the incident electron beamspermit the transmitted portions of the beams to excite phosphor elementsof the correct emissive color. A drawback of the shadow mask type CRT isthat the masking plate, at the center of the screen, intercepts all butabout 18-22% of the beam current; that is, the masking plate is said tohave a transmission of only about 18-22%. Thus, the area of theapertures in the plate is about 18-22% of the area of the masking plate.Since there are no focusing fields associated with the masking plate, acorresponding portion of the screen is excited by the electron beams.

In order to increase the transmission of the color selection electrodewithout increasing the size of the excited portions of the screen,post-deflection focusing color selection structures are required. Thefocusing characteristics of such structures permit larger apertureopenings to be utilized to obtain greater electron beam transmissionthan can be obtained with the conventional shadow mask. One suchstructure is described in Japanese Patent Publication No. SHO 39-24981by Sony, published on Nov. 6, 1964. In that structure, mutuallyorthogonal lead wires are attached at their crossing points byinsulators to provide large window openings through which the electronbeams pass. One drawback of such a structure is that individualelectrical connections, presumably, must be made to each of the leadwires to apply suitable potentials thereto. Another color selectionelectrode focusing structure that partially overcomes this drawback isdescribed in U.S. Pat. No. 4,443,499, issued on Apr. 17, 1984 to Lipp.The structure described in U.S. Pat. No. 4,443,499 utilizes a maskingplate with a plurality of rectangular apertures therethrough as thefirst electrode. Metal ridges separate the columns of apertures. Thetops of the metal ridges are provided with a suitable insulatingcoating. A metallized coating overlies the insulating coating to form asecond electrode that provides the required electron beam focusing whensuitable potentials are applied to the masking plate and to themetallized coating. Alternatively, as described in U.S. Pat. No.4,650,435, issued on Mar. 17, 1987 to Tamutus, a metal masking plate,which forms the first electrode, is etched from one surface to provideparallel trenches in which insulating material is deposited and built upto form insulating ridges. The masking plate is further processed bymeans of a series of photoexposure, development, and etching steps toprovide apertures between the ridges of insulating material that resideon the support plate. Metallization on the tops of the insulating ridgesforms the second electrode. In the structures described in the two U.S.Patents, one of the potentials required for the operation of the colorselection electrode can be applied directly to the masking plate;however, individual connections must be made to each of the secondelectrodes in order to apply a suitable potential thereto. Thus, a needexists for an efficient structure for making electrical connections tothe second electrodes.

SUMMARY OF THE INVENTION

The present invention relates to a color cathode-ray tube having anevacuated envelope with an electron gun therein for generating at leastone electron beam. The envelope further includes a faceplate panelhaving a luminescent screen with phosphor lines on an interior surfacethereof. A uniaxial tension focus mask, having a plurality ofspaced-apart first metal strands, is located adjacent to an effectivepicture area of the screen. The spacing between the first metal strandsdefines a plurality of slots substantially parallel to the phosphorlines of the screen. A plurality of second metal strands are orientedsubstantially perpendicular to the first metal strands and are insulatedtherefrom across the effective picture area. The second metal strandsare attached by a glass conductor layer to respective right and leftfirst metal end strands outside the effective picture area to formbusbars.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail, with relation tothe accompanying drawings, in which:

FIG. 1 is a plan view, partly in axial section, of a color CRT embodyingthe invention;

FIG. 2 is a plan view of a uniaxial tension focus mask-frame assemblyused in the CRT of FIG. 1;

FIG. 3 is a front view of the mask-frame assembly taken along line 3--3of FIG. 2;

FIG. 4 is an enlarged section of the uniaxial tension focus mask shownwithin the circle 4 of FIG. 2;

FIG. 5 is a section of the unlaxial tension focus mask and theluminescent screen taken along lines 5--5 of FIG. 4;

FIG. 6 is an enlarged view of a portion of the unlaxial tension focusmask within the circle 6 of FIG. 5; and

FIG. 7 is an enlarged view of another portion of the uniaxial tensionfocus mask within the circle 7 of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a color CRT 10 having a glass envelope 11 comprising arectangular faceplate panel 12 and a tubular neck 14 connected by arectangular funnel 15. The funnel has an internal conductive coating(not shown) that is in contact with, and extends from, a first anodebutton 16 to the neck 14. A second anode button 17, located opposite thefirst anode button 16, is not contacted by the conductive coating. Thepanel 12 comprises a cylindrical viewing faceplate 18 and a peripheralflange or sidewall 20 that is sealed to the funnel 15 by a glass frit21. A three-color luminescent phosphor screen 22 is carded by the innersurface of the faceplate 18. The screen 22 is a line screen, shown indetail in FIG. 5, that includes a multiplicity of screen elementscomprised of red-emitting, green-emitting, and blue-emitting phosphorlines, R, G, and B, respectively, arranged in triads, each triadincluding a phosphor line of each of the three colors. Preferably, alight absorbing matrix 23 separates the phosphor lines. A thinconductive layer 24, preferably of aluminum, overlies the screen 22 andprovides means for applying a uniform first anode potential to thescreen as well as for reflecting light, emitted from the phosphorelements, through the faceplate 18. A cylindrical multi-apertured colorselection electrode, or uniaxial tension focus mask, 25 is removablymounted, by conventional means, within the panel 12, in predeterminedspaced relation to the screen 22. An electron gun 26, shownschematically by the dashed lines in FIG. 1, is centrally mounted withinthe neck 14 to generate and direct three inline electron beams 28, acenter and two side or outer beams, along convergent paths through themask 25 to the screen 22. The inline direction of the beams 28 is normalto the plane of the paper.

The CRT of FIG. 1 is designed to be used with an external magneticdeflection yoke, such as the yoke 30, shown in the neighborhood of thefunnel-to-neck junction. When activated, the yoke 30 subjects the threebeams to magnetic fields that cause the beams to scan a horizontal andvertical rectangular raster over the screen 22. The uniaxial tensionmask 25 is formed, preferably, from a thin rectangular sheet of about0.05 mm (2 mil) thick low carbon steel, that is shown in FIG. 2 andincludes two long sides 32, 34 and two short sides 36, 38. The two longsides 32, 34 of the mask parallel the central major axis, X, of the CRTand the two short sides 36, 38 parallel the central minor axis, Y, ofthe CRT. The steel has a composition, by weight, of about 0.005% carbon,0.01% silicon, 0.12% phosphorus, 0.43% manganese, and 0.007% sulfur.Preferably, the ASTM grain size of the mask material is within the rangeof 9 to 10. The mask 25 includes an apertured portion that is adjacentto and overlies an effective picture area of the screen 22 which lieswithin the central dashed lines of FIG. 2 that define the perimeter ofthe mask 25. As shown in FIG. 4, the uniaxial tension focus mask 25includes a plurality of elongated first metal strands 40, each having atransverse dimension, or width, of about 0.3 mm (12 mils) separated bysubstantially equally spaced slots 42, each having a width of about 0.55mm (21.5 mils) that parallel the minor axis, Y, of the CRT and thephosphor lines of the screen 22. In a color CRT having a diagonaldimension of 68 cm (27 V), there are about 600 of the first metalstrands 40. Each of the slots 42 extends from the long side 32 of themask to the other long side 34, not shown in FIG. 4. A frame 44, for themask 25, is shown in FIGS. 1-3 and includes four major members, twotorsion tubes or curved members 46 and 48 and two tension arms orstraight members 50 and 52. The two curved members, 46 and 48, parallelthe major axis, X, and each other. As shown in FIG. 3, each of thestraight members 50 and. 52 includes two overlapped partial members orparts 54 and 56, each part having an L-shaped cross-section. Theoverlapped parts 54 and 56 are welded together where they areoverlapped. An end of each of the parts 54 and 56 is attached to an endof one of the curved members 46 and 48. The curvature of the curvedmembers 46 and 48 matches the cylindrical curvature of the uniaxialtension focus mask 25. The long sides 32, 34 of the uniaxial tensionfocus mask 25 are welded between the two curved members 46 and 48 whichprovide the necessary tension to the mask. Before welding to the frame44, the mask material is pre-stressed and darkened by tensioning themask material while heating it, in a controlled atmosphere of nitrogenand oxygen, at a temperature of about 500° C. for one hour. The frame 44and the mask material, when welded together, comprise a uniaxial tensionmask assembly.

With reference to FIGS. 4 and 5, a plurality of second metal strands 60,each having a diameter of about 0.025 mm (1 mil), are disposedsubstantially perpendicular to the first metal strands 40 and are spacedtherefrom by an insulator 62 formed on the screen-facing side of each ofthe first metal strands. The second metal strands 60 form cross membersthat facilitate applying a second anode, or focusing, potential to themask 25. The preferred material for the second metal strands is HyMu80wire, available from Carpenter Technology, Reading, Pa. The verticalspacing, or pitch, between adjacent second strands 60 is about 0.41 mm(16 mils). Unlike the cross members described in the prior art that havea substantial dimension that significantly reduces the electron beamtransmission of the masking plate, the relatively thin second metalstrands 60 provide the essential focusing function to the presentuniaxial focus tension mask 25 without adversely affecting the electronbeam transmission thereof. The uniaxial tension focus mask 25, describedherein, provides a mask transmission, at the center of the screen, ofabout 60%, and requires that the second anode, or focusing, voltage, ΔV,applied to second strands 60, differs from the first anode voltageapplied to the first metal strands 40 by less than about 1 kV, for afirst anode voltage of about 30 kV.

The insulators 62, shown in FIGS. 4 and 5, are disposed substantiallycontinuously on the screen-facing side of each of the first metalstrands 40. The second metal strands 60 are bonded to the insulators 62to electrically isolate the second metal strands 60 from the first metalstrands 40.

The method of making the uniaxial tension focus mask 25 includesproviding, e.g., by spraying, a first coating of an insulative,devitrifying solder glass onto the screen-facing side of the first metalstrands 40. A suitable solvent and an acrylic binder are mixed with thedevitrifying solder glass to give the first coating a modest degree ofmechanical strength. The first coating has a thickness of about 0.14 mm.The frame 44, to which the first metal strands 40 are attached, isplaced into an oven and the first coating is dried at a temperature ofabout 80° C. A devitrifying solder glass is one that melts at a specifictemperature to form a crystallized glass insulator. The resultantcrystallized glass insulator is stable and will not remelt when reheatedto the same temperature. After drying, the first coating is contoured sothat it is shielded by the first metal strands 40 to prevent theelectron beams 28, passing thought the slots 42, from impinging upon theinsulator and charging it. The contouring is performed on the firstcoating by abrading or otherwise removing any of the solder glassmaterial of the first coating that extends beyond the edge of thestrands 40 and would be contacted by either the deflected or undeflectedelectron beams 28. The first coating is entirely removed, by modestmechanical action, from the initial and ultimate, i.e., the right andleft first metal strands, hereinafter designated the first metal endstrands 140, before the first coating is heated to the sealingtemperature. The first metal end strands 140, which are outside of theeffective picture area, subsequently will be used as busbars to addressthe second metal strands 60. To further ensure the electrical integrityof the uniaxial tension focus mask 25 by minimizing the possiblity of ashort circuit, at least one additional first metal strand 40 is removedbetween the first metal end strands 140 and the first metal strands 40that overlie the effective picture area of the screen. Thus, the rightand left first metal end strands 140, outside the effective picturearea, are spaced from the first metal strands 40 that overlie thepicture area by a distance of at least 1.4 mm (55 mils), which isgreater than the width of the equally spaced slots 42 that separate thefirst metal strands 40 across the picture area.

The frame 44 with the first metal strands 40 and the metal end strands140 attached thereto (hereinafter referred to as the assembly) is placedinto an oven and heated in air. The assembly is heated over a period of30 minutes to a temperature of 300° C. and held at 306° C. for 20minutes. Then, over a period of 20 minutes, the temperature of the ovenis increased to 460° C. and held at that temperature for one hour tomelt, and crystallize the first coating to form a first insulator layer64 on the first metal strands 40, as shown in FIG. 6. The resultantfirst insulator layer 64, after firing, has a thickness within the rangeof 0.5 to 0.9 mm (2 to 3.5 mils) across each of the strands 40. Thepreferred solder glass for the first coating is a lead-zinc-borosilicatesolder glass that melts in the range of 400° to 450° C. and iscommercially available, as SCC-11, from a number of glass suppliers,including SEM-COM, Toledo, Ohio, and Coming Glass, Coming, N.Y.

Next, a second coating of a suitable insulative material, mixed with asolvent, is applied, e.g., by spraying, to the first insulator layer 64.Preferably, the second coating is a non-devitrifying (i.e., vitreous)solder glass having a composition of 80 wt. % PbO, 5 wt % ZnO, 14 wt. %B₂ O₃, 0.75 wt. % SnO₂, and, optionally, 0.25 wt. % CoO. A vitreousmaterial is preferred for the second coating because when it melts, itwill fill any voids in the surface of the first insulator layer 64without adversely affecting the electrical and mechanicalcharacteristics of the first layer. Alternatively, a devitrifying solderglass may be used to form the second coating. The second coating isapplied to a thickness of about 0.025 to 0.05 mm (1 to 2 mils). Thesecond coating is dried at a temperature of 80° C. and contoured, aspreviously described, to remove any excess material that could be struckby the electron beams 28.

As shown in FIGS. 4, 5 and 7, a thick coating of a devitrifying solderglass containing silver, to render it conductive, is provided on thescreen-facing side of the left and right first metal end strands 140. Aconductive lead 65, formed from a short length of nickel wire, isembedded into the conductive solder glass on one of the first metal endstrands. Then, the assembly, having the dried and contoured secondcoating overlying the first insulator layer 64, has the second metalstrands 60 applied thereto so that the second metal strands overlie thesecond coating of insulative material and are substantiallyperpendicular to the first metal strands 40. The second metal strands 60are applied using a winding fixture, not shown, that accuratelymaintains the desired spacing of about 0.41 mm between the adjacentsecond metal strands. The second metal strands 60 also contact theconductive solder glass on the first metal end strands 140.Alternatively, the conductive solder glass can be applied at thejunction between the second metal strands 60 and the first metal endstrands 140 during, or after, the winding operation. Next, the assembly,including the winding fixture, is heated for 7 hours to a temperature of460° C. to melt the second coating of insulative material, as well asthe conductive solder glass, to bond the second metal strands 60 withinboth a second insulator layer 66 and to a glass conductor layer 68. Thesecond insulator layer 66 has a thickness, after sealing, of about 0.013to 0.025 mm (0.5 to 1 mil). The height of the glass conductor layer 68is not critical, but should be sufficiently thick to firmly anchor thesecond metal strands 60 and the conductive lead 65 therein. The portionsof the second metal strands 60 extending beyond the glass conductorlayer 68 are trimmed to free the assembly from the winding fixture.

The first metal end strands 140 are severed at the ends adjacent to longside or top portion 32, shown in FIG. 4, and long side or bottom portion34 (not shown) of the mask 25 to provide a gaps of about 0.4 mm (15mils) therebetween that electrically isolate the first metal end strands140 and forms busbars that permit a second anode voltage to be appliedto the second metal strands 60 when the conductive lead 65, embedded inthe glass conductor layer 68, is connected to the second anode button17.

What is claimed is:
 1. In a color cathode-ray tube comprising anevacuated envelope having therein an electron gun for generating atleast one electron beam, a faceplate panel having a luminescent screenwith phosphor lines on an interior surface thereof, and a uniaxialtension focus mask, wherein the improvement comprisingsaid uniaxialtension focus mask having a plurality of spaced-apart first metalstrands which are adjacent to an effective picture area of said screenand define a plurality of slots substantially parallel to said phosphorlines, said first metal strands being formed from a thin metal sheethaving imperforate top and bottom portions, said right and left firstmetal end strands each having top and bottom ends separated from saidtop and bottom portions of said metal sheet by gaps to electricallyisolate said right and left first metal end strands; and a plurality ofsecond metal strands oriented substantially perpendicular to said firstmetal strands and insulated therefrom across said effective picturearea, said second metal strands being attached by a glass conductorlayer to said right and left first metal end strands outside of saideffective picture area to form busbars.
 2. The tube as described inclaim 1, further including a conductive lead embedded in said glassconductor layer of one of said first metal end strands outside saideffective picture area.
 3. The tube as described in claim 1, whereinsaid right and left first metal end strands outside said effectivepicture area are spaced from first metal strands across said effectivepicture area by a distance greater than the spacing of said slots acrosssaid effective picture area.